Evaporant holder



March 4, 19 39 c. R. sPrrzE 3,430,937

' EVAPORANT HOLDER Filed Feb. 17, 1966 INVENTOR CARY R. SPITZER 6 ATTORNEYS United States Patent ABSTRACT OF THE DISCLOSURE A resistively heated evaporant holder formed of a shaped metal foil and being provided with a laminated protective coating of nickel alumina and a ceramic overcoat on the reservoir portion of said holder with integral conductive tabs extending from opposite ends of the res ervoir portion.

The invention described herein Was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates generally to an evaporant holder and relates with particularity to a boat to hold small quantities of evaporant material while being evaporated in high vacuum evaporating systems in a temperature range of 200-1,320 C. for coatings and the like. Previously, stamped metal forms, twisted wire filaments, and ceramic crucibles with external heaters have been used to hold the evaporant material in high vacuum evaporator systems. Using resistively heated metal forms and twisted wire filaments causes problems in evaporating certain metals and inorganic compounds due to chemical reactions at elevated temperatures between the evaporant and the evaporant holder. To solve this problem, ceramic crucibles with the evaporant charge being disposed in side of the crucible and externally disposed resistively heated wires were devised. These proved generally satisfactory, however, the poor thermal contact between the crucible and heater and the fragileness of the crucible added to the numerous problems encountered in their use. More specifically, the use of externally resistively heated crucibles presents the hazard of breaking the crucible and losing the evaporant or being unable to attain adequate temperatures necessary to cause maximum evaporation of the evaporant material employed.

The present invention combines the advantageous features of the prior are devices while minimizing the disadvantages thereof to thereby provide the versatility of chemical inertness shown by a crucible coupled with the simplicity of metal formed or twisted wire filaments. The contact problem in the present invention is minimized since the ceramic coating is sprayed directly onto the foil heater. In addition, the ceramic holder of the present invention is quite strong and durable since it is backed by the foil material.

Accordingly, it is an object of the present invention to provide a new and novel resistively heated, chemical inert, evaporant boat.

Another object of the present invention to to provide a new and improved evaporant boat having an integral resistively heating system therein.

Yet another object of the present invention is a unitary structure for a resistively-heated evaporant boat in which a durable, chemically inert evaporant holder space is employed.

According to the present invention, the foregoing and other objects are obtained by cutting and bending, from a suitable refractory metal foil, blanks in the shape of the desired evaporant boat and placing the blanks in a 3,430,937 Patented Mar. 4, 1969 mount with clamps over the tab ends thereof. The mounted blanks are then flame-sprayed lightly with nickel alumina to clean the foil surface to be ceramic coated and to act as a bonding agent between the ceramic and the metal foil. A suitable ceramic is then flame-sprayed onto the nickel alumina surface to provide an adequate thickness of ceramic material to insure chemical inactivity of the evaporant and foil material during the evaporating process.

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily apparent as the same becomes better understood with reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a view of an exemplary shaped evaporant boat according to the present invention;

FIG. 2 is a View along lines 2-2 of FIG. 1 showing the coated layers of the evaporant boat; and,

FIG. 3 is an enlarged sectional view taken along lines 3-3 of FIG. 2, more clearly illustrating the nickel alumina and ceramic coating over the metallic foil boat.

Referring now to the drawings, and more particularly to FIG. 1, there is shown an evaporant holder, or evaporant boat, generally designated by reference numeral 11. Boat 11 includes an evaporant reservoir or chamber 13 and a pair of terminal tabs designated by reference numerals 15 and 17.

Referring now more particularly to FIGS. 2 and 3, it is readily apparent that the evaporant chamber 13 comprises the metal foil center portion 19 and a laminated coating consisting of layers 21 and 23 thereon. Layer 21 is a thin layer of nickel alumina while layer 23 is a ceramic coating applied to the nickel alumina inner layer, as will be more clearly explained hereinafter.

METHOD OF MAKING The evaporant holder or boat 11 is manufactured by a very simple but reliable process. The desired basic shape of the boat 11 is cut and bent from a suitable refractory metal foil, such for example 0.002-inch tantalum- 10% tungsten alloy. These blanks are then placed in a suitable mount, not shown, which clamps tabs 15 and -17 in protective position. This clamping serves two purposes, namely, it keeps the blank from moving while being treated and flame-sprayed and it keeps the ceramic off of the tabs to permit them to be used as electrical contacts when boat 11 is installed in the vacuum chamber. The mounted blanks are then sprayed with a light coating of nickel alumina. The nickel alumina serves to clean the surface of the metal foil and serves as a bonding agent between the ceramic and the metal foil. The ceramic is then sprayed on the foil in a conventional manner. One suitable apparatus for applying both the nickel alumina and the ceramic is a KD Flame Spray Machine manufactured by the Metro Company of Westbury, NY. After spraying with the ceramic, the boats are removed from the mount and are ready for immediate use. The ceramic coating 23 may be any one of or a combination of zirconium oxide (Zro chromium oxide (Cr O aluminum oxide (A1 0 or zirconium silicate (ZrSiO In use of the present invention the evaporant boat is, as described hereinbefore, installed in the vacuum furnace from which a suitable evaporant is to be evaporated with tabs 15 and 17 serving as the electrical contacts to provide resistance heating for boat 11 in a conventional manner. The evaporant material is placed in the evaporant chamber 13 and, due to the chemical inertness of the evaporant and the ceramic coating, no chemical reaction occurs during the evaporating process. The combined thickness of the nickel alumina and the ceramic employed is essentially in the range of 0.015 and 0.030-inch.

Although the invention has been described relative to a particular shape for the evaporant boat 11, it is readily apparent to those skilled in the art that the boat could be formed of any suitable shape and size depending upon the quantity of evaporant material intended to be employed. For example, the chamber 13 may be made from a metal foil blank by merely stamping the desired depression in the foil and then coating the foil sections as described hereinbefore. In addition, a suitable twisted wire filament formed in helixes to form a crucible may be flame-sprayed with the nickel alumina inner coat and the ceramic outer coat to provide a suitable resistance heating crucible. Also, although the invention has been described relative to a particular metal foil it is obvious to those skilled in the art that other suitable electrically conductive foils may be employed in making the evaporant boat according to the present invention.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A resistively heated evaporant holder or boat comprising:

a refractory metal foil cut and bent so as to form an evaporant reservoir and a pair of exposed conductive tabs integrally exterior of said reservoir,

said reservoir portion of said formed foil being provided with a laminated protective coating, said coating including a first layer of nickel alumina and a second layer of ceramic.

2. The evaporant boat of claim 1 wherein said metal foil is a tantalum-tungsten alloy.

3. The evaporant boat of claim 2 wherein said foil has a thickness of approximately 0.002-inch and the combined thickness of said first and second layers is in the range of 0.015 and 0.030-inch.

4. The evaporant boat of claim 1 wherein said first layer of nickel alumina is flame-sprayed onto said formed foil to serve as a cleaning agent for said foil and as a bonding agent for said ceramic coating.

5. The evaporant boat of claim 1 wherein said ceramic layer is selected from the group of ceramics consisting of ZIOZ, crzog, A1203 and ZISiOiQ.

6. The evaporant boat of claim 1 wherein said coating is designed to resist degradative chemical and physical reactions when exposed to an elevated temperature and reduced pressure environment, said coating being made up of individual flame-sprayed layers of nickel alumina and a ceramic.

References Cited UNITED STATES PATENTS JOHN J. CAMBY, Primary Examiner. 

